Retrieval device made of precursor alloy cable

ABSTRACT

A medical retrieval device for retrieving foreign objects from a patient and the method of constructing the device are disclosed. The device incorporates a wire cable composed of a precursor alloy to a superelastic material to improve durability of the device. Because precursor alloys exhibit, a linear stress-strain relationship and a yield point associated with a relatively high stress level, the device transfers greater stresses before experiencing deformation. Thus, greater crushing forces can be achieved using a device of this type. These crushing forces may be needed when the foreign object is too large to remove intact. This property also facilitates the device in dilating ducts to retrieve foreign objects. Using the precursor alloy additionally eliminates the need for heat treatment of the cables used in constructing the device. A retrieval device made of precursor alloy cable also is less susceptible to permanent deformation and unwinding during use.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/679,563 filed Oct. 6, 2003, which is a divisional of U.S. applicationSer. No. 10/341,170 filed Jan. 13, 2003, which is a continuation of U.S.application Ser. No. 10/135,006 filed Apr. 30, 2002, now U.S. Pat. No.6,814,740, which is a continuation of U.S. application Ser. No.09/801,186 filed Mar. 8, 2001, now U.S. Pat. No. 6,402,761, which is acontinuation of U.S. application Ser. No. 09/427,553 filed Oct. 27,1999, now U.S. Pat. No. 6,217,589.

FIELD OF THE INVENTION

The present invention pertains to a medical device used to extractforeign objects from a patient. More specifically, the invention relatesto an endoscopic device used to retrieve, crush, and remove gallstonesand the like. The device is designed to traverse through narrow passageswithin the body and to open within those passages to retrieve theforeign object.

BACKGROUND OF THE INVENTION

The removal of foreign bodies from patients often requires the use ofendoscopic devices. In particular, gastroenterologists commonly usegrasping or crushing devices to extract stones from a patient's biliaryduct. Additionally, snares are often used when removing stents or otherforeign objects.

Grasping and crushing devices generally take the form of wire basketsthat deploy to capture the stone to be extracted. These wire baskets maybe used for lithotripsy if the stone is too large to be removed intact.Lithotripsy involves crushing the stone into fragments to facilitateremoval prom the duct. Effective performance of such devices requiresthe baskets to have enough flexibility to be inserted into the commonbile duct. However, the baskets also must have a certain degree ofrigidity to dilate the duct to facilitate stone capture. Often, thebaskets are deployed using a retaining cannula. In this case, thecannula retains the basket in a retracted configuration during insertioninto the bile duct. Once within the grasping region of a stone, thebasket extends from the cannula and opens to capture the stone. In sucha case, the basket must have enough stiffness to open the duct whenremoved from the cannula, without being so stiff that it is permanentlydeformed due to retention within the cannula.

Aside from deformation associated with dilating the duct or retentionwithin the cannula, a common failure of conventional baskets occursduring lithotripsy when the baskets are subject to forces often inexcess of 50 pounds. Under such force, the basket can become severelydeformed, rendering it unsuitable for repeated use. Such repeated use isdesirable because of the frequent occurrence of the need to remove morethan one stone or other object at a time from the patient. Therefore,design of these devices includes focus on the durability of the basketin repeated use settings.

To repeatedly crush and retrieve foreign objects, a basket must beflexible enough to traverse tortuous anatomy, yet stiff enough to openwithin a duct, and strong enough to crush stones. A single wireconstruction may meet any one of these criteria, but typically cannotmeet all three requirements for repeated dilation and lithotripsy. Ithas been proposed, therefore, to construct a retrieval basket of astranded cable, such as stainless steel cable. Purely stainless steelcable (the core and strands) may work well for the extraction of asingle stone, but is subject to the deformation problems discussedpreviously when used for repeated dilatation or lithotripsy.

Other baskets are formed from cable which includes a superelastic,sometimes referred to as shape memory, core wrapped with strands ofstainless steel to surround the core. Nitinol is often used as thesuperelastic core in these devices. Nitinol is a specially heat-treatedTitanium-Nickel (Ti—Ni) alloy, preferably approximately 55%/45% Nickelto Titanium (Ni—Ti). These baskets require heat treatment for the coreto retain its shape. Such a configuration allows for some improvement inperformance when the baskets are used repeatedly and for lithotripsybecause the superelastic core better retains its shape.

However, superelastic materials of this type experience phasetransformations when subject to a certain level of stress loading.Lithotripsy often reaches these stress levels. Upon a phasetransformation, the core of the cable stretches, rendering the deviceincapable of transferring force to the stone to complete the crushingprocess. Furthermore, the superelastic alloy has a greater reversibleelongation than do the surrounding stainless steel strands. This resultsin a difference in deformation between the core and the surroundingstrands leading to a permanent deformation of the cable. Suchdeformation results in an alteration of the basket shape, making it lessdesirable to use for its intended purpose.

Moreover, manufacturing both the cable core and strands fromsuperelastic alloy wires results in a cable that unwinds due to thehighly elastic, nature of the material. Thus, a retrieval basket of suchcable also will not retain its desired shape without heat treating.

SUMMARY OF THE INVENTION

The advantages and purpose of the invention will be set forth in part inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Theadvantages and purpose of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

To attain the advantages and in accordance with the purpose of theinvention, as embodied and broadly described herein, the inventionincludes a medical retrieval device for retrieving foreign objects fromwithin a patient's body. The retrieval device includes a retrievalassembly containing a cable preformed into a configuration for capturingand removing the foreign object. The retrieval cable includes wire madeof a precursor alloy to a superelastic material. According to aparticularly preferred embodiment of the invention, the cable includes acore wire and surrounding wire strands, each made of the precursoralloy.

The invention further includes a method of manufacturing the medicalretrieval device including the steps of constructing a cable including awire made of a precursor alloy to a superelastic material and forming aretrieval assembly by preforming the cable into a configuration adaptedto capture and remove the foreign objects.

The precursor alloy according to the present invention exhibits astress-strain curve having a linear relationship extending through ayield point with no phase transformation point. After the yield point,the stress-strain curve does not exhibit a substantially constant stressplateau as strain increases. Rather, the precursor alloy exhibitsplastic deformation properties.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate the preferred embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 a is a stress-strain curve for a superelastic alloy;

FIG. 1 b is a stress-strain curve for a precursor alloy;

FIG. 2 a is a cross-sectional view of one embodiment of a strandingconfiguration according to the present invention, wherein a core ofprecursor alloy is surrounded by strands of stainless steel wires;

FIG. 2 b is a cross-sectional view of another embodiment of a strandingconfiguration according to the present invention, wherein a core ofprecursor alloy is surrounded by strands of precursor alloy wire; and

FIG. 3 is a wire basket retrieval device according to an embodiment ofthe present invention and in a deployed position for retrieving anobject.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The various aspects of this invention generally pertain to a device, anda method for manufacturing such a device, for retrieving foreign objectsin a body from locations requiring traversal of narrow passages. In use,such a device must be able to collapse into a relatively narrow spacefor traversal purposes and to expand in that space for retrievalpurposes. The device also must have strength characteristics so that thedevice can crush objects to facilitate capturing and removal.Additionally, the device must reconfigure to it original shape whenexpanded and retain its ability to reconfigure to the original shape forrepeated deployments without losing strength and without sufferingpermanent deformation.

To accomplish these objectives and to overcome the problems associatedwith existing devices of this kind, a retrieval device of the presentinvention incorporates a precursor alloy into the stranded cable usedfor making the device. When subject to heat treatment, a precursor alloyresults in the formation of a superelastic alloy. Prior to heattreatment, such a precursor alloy exhibits high elongation and a linearstress-strain relationship with a yield point. Because of theseproperties, the use of a precursor alloy in the manufacture of thedevice according to the present invention achieves greater strength,longer life, and ease in manufacture, as will be explained.

Unlike a superelastic alloy, a precursor alloy used in a medicalretrieval device of the present invention exhibits a linearstress-strain relationship with a plastic yield point. For comparisonpurposes, schematics of the stress-strain curves for a superelasticalloy and a precursor alloy are shown in FIGS. 1 a and 1 b,respectively. As shown in FIG. 1 a, as a superelastic alloy undergoesincreased stress, strain increases to phase transformation point X. AtX, the superelastic alloy transforms from an austenitic phase to amartensitic phase. Thereafter, stress remains substantially constant asstrain increases, forming a substantially constant stress plateau P.Upon releasing the stress on the superelastic alloy, the reversiblydeformable nature of the material allows it to return to its originallength following curve Y in the Figure. The cycle shown often occursrepeatedly with no appreciable change in dimension or plasticdeformation of the wire. Therefore, the superelastic alloy withstands arelatively large strain prior to the phase transformation point, andadditional strain during the phase transformation, without plasticdeformation. Furthermore, the phase transformation and reversibledeformation of the superelastic alloy occurs at relatively low stresslevels. During the superelastic alloy phase transformation, appliedstress is absorbed by the alloy to facilitate the phase transformation,and is not available to be transferred to another object, such as astone.

A precursor alloy material exhibits the stress-strain characteristicsshown in FIG. 1 b. Up to the plastic yield point Z, strain increases ina reversible manner as stress increases. That is, the precursor alloyreturns to its normal configuration upon release of stresses prior toreaching plastic yield point Z. Moreover, the precursor alloy does notpass through a substantially constant stress plateau as does thesuperelastic alloy. At stresses above yield point Z, the precursor alloybecomes plastically and irreversibly deformed, unlike the superelasticalloy. As shown in FIGS. 1 a and 1 b, yield point Z of the precursoralloy generally occurs at higher stress levels than does phasetransformation point X of the superelastic material. This enables thedevice of the present invention to transfer greater stress to stonesduring lithotripsy, as well as facilitating dilation of ducts.Accordingly, the inventive devices facilitate retrieval and removal,while maintaining shape and strength over repeated uses.

In addition to requiring heat treatment of the precursor alloy toproduce the superelastic material, a conventional retrieval device alsorequires heat treatment during the formation of the basket so that thesuperelastic wires maintain their shape. In contrast, a result of theplastic yield point associated with a precursor alloy, the basket of thepresent device forms easily by mechanically bending the precursor alloywire beyond its yield point and into shape. Sophisticated heattreatments are thus unnecessary in the manufacture of the inventivedevice.

Moreover, because of the superelastic nature of the heat-treated alloysused in conventional devices, a stranded cable made entirely of asuperelastic material is ineffective due to phase transformationdeformation and unwinding problems, as mentioned above. However,precursor alloys are highly elastic but also can be plasticallydeformed. Thus, in a preferred embodiment of the present invention, acable for a retrieval device is made entirely of a precursor alloy coreand precursor alloy strands. It is contemplated that the strands and thecore can be made of identical precursor alloy or different precursoralloys. If different precursor alloys are used, it is preferred toselect wire dimensions and types such that the wires exhibit similardeformations when subjected to a given load. In either case, the cablewill experience neither unwinding nor excessive deformation as would acable that includes superelastic strands. Furthermore, using aconsistent material configuration for both the strands and the corewould eliminate problems associated with elongation of the core relativeto the surrounding strands leading to permanent damage to the basket.Finally, a cable made entirely of wires of the same precursor alloymaterial facilitates the manufacturing process.

Reference will now be made in detail to the present exemplaryembodiments of the invention, examples of which ate illustrated in FIGS.2 and 3. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

In accordance with embodiments of the present invention, an endoscopicretrieval device 5 is formed from a stranded cable having the basicconfiguration shown in either FIG. 2 a or FIG. 2 b. FIG. 2 a shows across-section of cable of a first embodiment of the device 5. A cable 1includes a core monofilament wire 2 made of precursor alloy. Surroundingcore wire 2 are strands 3 of stainless steel wire. Due to the presenceof the precursor alloy core wire 2, device 5 suffers from lessdeformation problems than does a conventional device of this type thatincludes a superelastic core. This is because, as previously discussed,precursor alloys exhibit less elongation than do superelastic materialsand therefore differences in the elongation between surrounding strands3 and core wire 2 will be minimized.

FIG. 2 b shows a more preferred embodiment of a stranded cable for usein the endoscopic retrieval device 5. In this embodiment, a cable 1′includes a core wire 2′ made of a precursor alloy as in FIG. 2 a.However, surrounding strands 3′ in this embodiment also are formed ofprecursor alloy, either of identical or different precursor alloymaterial as core wire 2′. As discussed previously, this embodiment ispreferred because the cables made entirely of precursor alloy wires(core and strands) will not unwind and are capable of transferringgreater stress to objects without deforming. Additionally, cables madeof entirely of the same precursor alloy alleviate deformation problemsassociated with different rates of elongation between the core andstrands. When selecting wires of different precursor alloys, it ispreferable to impart consistent mechanical properties to the cable. Aperson having ordinary skill in the art would realize that suchconsistency can be achieved by varying such factors as, for example, thenature of the alloys of the surrounding strands and core wire, relativedimensions of the core wire and the surrounding strands, the windingpattern of the strands around the core wire, and the post processing ofthe cable.

FIGS. 2 a and 2 b show six surrounding wire strands 3 and 3′,respectively. Preferably, there are at least five surrounding wirestrands 3 or 3′. However, it is contemplated that the number ofsurrounding strands can be varied in accordance with the particular usefor the device or the desired characteristics of the cable.

In both FIGS. 2 a and 2 b, the precursor alloy is in a martensitic phaseat room temperature to body temperature. The precursor alloy can, be aprecursor Nitinol or other material exhibiting like properties and knownto those having ordinary skill in the art. Such other precursor alloysthat may be used include, for example, Silver-Cadmium, Gold-Cadmium,Gold-Copper-Zinc, Copper-Zinc, Copper-Zinc-Aluminum, Copper-Zinc-Tin,Copper-Zinc-Xenon, Iron-Beryllium, Iron-Platinum, Indium-Thallium,Iron-Manganese, Nickel-Titanium-Vanadium, Iron-Nickel-Titanium-Cobalt,and Copper-Tin.

In one preferred form of the invention, the overall diameter of thecable is approximately 0.017 inches. The materials used for theprecursor alloy, the number of strands forming the cable, and theoverall diameter of the cable can be modified according to theparticular use or desired characteristics of the device. The selectionof these parameters would be obvious to one having ordinary skill in theart.

FIG. 3 shows the overall construction of endoscopic retrieval device 5.Typically, four cables 1 or 1′ form basket 6. However, any number ofcables can be used and would be obvious to one having ordinary skill inthe art depending on the use or desired characteristics of the basket. Abullet-shaped nosepiece 7 can be attached to a distal end of device 5 toimprove guidance of device 5 during use, as well as to secure cables 1or 1′ to each other. A coupling tube 8, attached to a proximal end ofbasket 6, also facilitates manipulation of device 5 during the retrievalprocess. Coupling tube 8 also could take the form of a cannula, in whichcase basket 6 would retract into the cannula prior to retrieval.

Laser welding represents one preferred mode of attachment ofbullet-shaped nosepiece 7 and coupling tube 8 to basket 6. However,other suitable attachment methods known to those skilled in the art arewithin the scope of the present invention. Device 5 is used to traversenarrow passages to retrieve, crush, and remove foreign objects withinthe body. Device 5 can be deployed from a cannula or traverseindependently through the body, collapsing and deploying as necessary.Device 5 also may be used repeatedly to retrieve, crush, and removeforeign objects.

The manufacture of device 5 first involves forming cables 1, 1′. To formthese cables, a precursor alloy wire is supplied as the core wire andsurrounding strands of wire are placed approximately evenly-spacedaround the perimeter of the core wire. Surrounding strands wrap aroundthe core in an essentially helical fashion along its length. The strandscan be wrapped clockwise, counterclockwise, or any combination thereof,depending on the desired properties of the cable. A preferred embodimenthas strands wrapping clockwise around the core wire, similar to threadsof a right-hand screw. The cable can then be rotary swaged, which helpsto straighten it and increase its column strength. As discussed withreference to FIGS. 2 a and 2 b, the surrounding strands can be made ofstainless steel or other like, suitable material, or most preferablyprecursor alloy.

Several cables, preferably approximately four cables 1 or 1′, are thenbent past the yield point of either the precursor alloy or stainlesssteel to form basket 6. After forming basket 6, cables 1 or 1′ arejoined together at one end, through welding or other suitable joiningmethod known to those skilled in the art. Laser welding cables 1 or 1′to coupling tube 8 or, if desired, to the retractable portion of aretaining cannula, represents another method to connect and secure thecables to each other. As discussed with reference to FIG. 3, a nosepiececan be laser welded, or otherwise attached in any suitable manner, tothe end of basket 6 to guide device 5 through the body. It is importantthat during welding or other connecting operations involving heat, thattemperature is controlled to prevent heat treating the cable such thatthe precursor alloys are converted to superelastic materials.

The stranded cable configuration used in the retrieval device accordingto the present invention provides the durability necessary to performlithotripsy and dilation and be repeatedly employed for retrievalprocesses. Incorporating precursor alloy wire into the cable as opposedto a superelastic material such as Nitinol enables the device to bemanufactured without heat treatment processes. Additionally, becauseprecursor alloys do not exhibit the extreme elongation characteristic ofsuperelastic materials, problems of permanent deformation are alleviatedwhen surrounding stainless steel wire strands are used to form thecable. Using precursor alloys also allows for the manufacture of a cablecomprised entirely of precursor alloy wire, including the surroundingstrands and the core. Whether identical precursor alloy is used forboth, or the precursor alloy used for the strands differs from that usedfor the core, the device will be capable of transferring greater stressto objects without deformation and will not unwind. Additionally, usingthe same precursor alloy for both the strands and the core facilitatesoverall manufacture of the device and provides a device of consistentcharacteristics that will not deform due to disparate elongationproperties within the cables.

Although the use of a basket type retrieval device has been discussedand shown in the Figures, it is contemplated that the device can be ofthe snare type. A snare made of the precursor alloys discussed abovewould retain its shape better than conventional stainless steel snaredevices. Furthermore, although most of the above discussion pertains tousing the inventive device to remove gallstones, it should beappreciated that the devices can be used for removing a variety of otherforeign objects having various locations within the body.

It will be apparent to those skilled in the art from consideration ofthe specification and practice of the invention disclosed herein thatvarious modifications and variations can be made in the endoscopicretrieval device formed of precursor alloy cable of the presentinvention. Therefore, the invention in its broader aspects is notlimited to the specific details and illustrative examples shown anddescribed in the specification. It is intended that departures may bemade from such details without departing from the true spirit or scopeof the general inventive concept as defined by the following claims andtheir equivalents.

1. A medical device comprising: a coupling tube having a proximal endand a distal end; a nosepiece; and a plurality of cables having a firstend and a second end, wherein said first end of each cable is fixedlyattached to the nosepiece and the second end is operably coupled to thecoupling tube, wherein each of the plurality of cables further comprisesa plurality of wire strands at least one strand of which comprises aprecursor to a superelastic alloy, said alloy having the property ofhaving a substantially linear stress-strain curve in such that thestrain increases in a reversible manner as stress increases up to aplastic yield at which stress permanent plastic deformation occurs;wherein each of the plurality of cables has a first configuration inwhich the cable is collapsed into a narrow space and a secondconfiguration in which the cable is expanded such that the plurality ofcables form a basket.
 2. The medical device of claim 1, wherein theoperable coupling of the second ends of the plurality of cables to thecoupling tube comprises a fixed attachment thereto.
 3. The medicaldevice of claim 1, wherein the coupling tube has a lumen therethroughextending from the distal end to the proximal end thereof.
 4. Themedical device of claim 3, wherein the operable coupling of the secondends of the plurality of cables to the coupling tube comprises passingthe plurality of cables through the lumen of the coupling tube.
 5. Themedical device of claim 1, wherein the plurality of wire strands withina cable comprises a core strand and a plurality of strands surroundingthe core strand.
 6. The medical device of claim 5, wherein the at leastone strand which comprises a precursor to a superelastic alloy is a corestrand.
 7. The medical device of claim 5, wherein all of the strands ofthe plurality of strands comprises a precursor to a superelastic alloy.8. The medical device of claim 5, wherein the surrounding strands arewrapped around the core strand in a clockwise manner.
 9. The medicaldevice of claim 5, wherein the surrounding strands are wrapped aroundthe core strand in a counterclockwise manner.
 10. The medical device ofclaim 5, wherein the plurality of wire strands within a cable are rotaryswaged.
 11. The medical device of claim 1, wherein the precursor to asuperelastic alloy is selected from the group consisting ofSilver-Cadmium, Gold-Cadmium, Gold-Copper-Zinc, Copper-Zinc,Copper-Zinc-Aluminum, Copper-Zinc-Tin, Copper-Zinc-Xenon,Iron-Beryllium, Iron-Platinum, Indium-Thallium, Iron-Manganese,Nickel-Titanium-Vanadium, Iron-Nickel-Titanium-Cobalt, Copper-Tin, andNickel-Titanium.
 12. The medical device of claim 1, wherein theprecursor to a superelastic alloy is a Nickel-Titanium alloy.
 13. Themedical device of claim 1, wherein the basket is capable of withstandinga longitudinal force of at least 50 pounds without permanentdeformation.
 14. The medical device of claim 1, further comprising acannula sized and adapted to receive the coupling tube with in the lumenthereof.